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Bad Gas Valve

I am always leary of changing a gas valve out, especially when it requires pulling the fireplace to do so.

Warnock-Hersey, the thermocouple is on the back of the dang valve so I didnt test mv, but it is enough to hold the pilot. Problem is when the gas valve knob is turned to On (rotated from pilot to on), it drops out. Gen is putting out 400-420 mv disconnected from system, about the same connected...

Dirty/lazy pilot, is the pilot being pulled away from the thermocouple when main burner ignites? You need to clean it up and get thermocouple readings, I know some of those units can be a pain in the neck to access to install adapter for testing but be patient you'll eventually get it.

Dirty/lazy pilot, is the pilot being pulled away from the thermocouple when main burner ignites? You need to clean it up and get thermocouple readings, I know some of those units can be a pain in the neck to access to install adapter for testing but be patient you'll eventually get it.

The MAIN BURNER cannot ignite, the pilot instantly drop s out when the valve is turned from PILOT to ON.

Does the pilot flame drop out instantly when you turn on the main burner, or does it get really small and then within a few seconds goes out completely? If that happens, then there is probably a pressure or volume problem within the gas valve or the gas line leading to the valve.

If the pilot flame is not hitting the TC properly, you can have very low voltage going to the electromagnet in the safety pilot system within the gas valve. The electromagnet will have enough stregnth to barely hold the pilot valve open, and when you turn the main knob it jars the valve slightly causing it to release. You really need to test the TC voltage.

The pilot drops out the instant the knob is moved from pilot of on, as soon as it leaves the pilot position. That seems like a valve issue to me, but thats why I am asking. I mean the pilot holds fine, until the instant I move the control knob... I dont see a ton of fireplace work, thankfully, but in all that I have seen, even ones brand new, thermopiles never put out more than 500 mv, even the ones that say 750 max... My understanding is hat most valves need about 250 mv to actually hold the gas valve coil...